Processability of silica-reinforced rubber containing an amide compound

ABSTRACT

The invention provides an amide compound as a processing aid to improve the dispersion of silica reinforcing filler in a rubber composition, while reducing or eliminating the use of expensive bifunctional silica coupling agents. The invention further provides a vulcanizable elastomeric composition and vulcanized elastomeric products, especially pneumatic tires that exhibit decreased rolling resistance, hysteresis, and improved snow, ice, and wet traction.

FIELD OF THE INVENTION

The invention relates generally to the use of processing aids to improvethe dispersion of silica reinforcing filler in rubber compounds. Moreparticularly, the invention provides a vulcanizable elastomericcomposition containing a filler-dispersing aid, and a pneumatic tirehaving improved snow and ice traction, wet traction, rolling resistanceand hysteresis.

BACKGROUND OF THE INVENTION

When producing elastomeric compositions for use in rubber articles, suchas tires, power belts, and the like, it is desirable that theseelastomeric compositions are easily processable during compounding andhave a high molecular weight with a controlled molecular weightdistribution, glass transition temperature (T_(g)) and vinyl content. Itis also desirable that reinforcing fillers, such as silica and/or carbonblack, be well dispersed throughout the rubber in order to improvevarious physical properties, such as the compound Mooney viscosity,elastic modulus, tan delta (δ), and the like. Rubber articles,especially tires, produced from vulcanized elastomers exhibiting theseimproved properties will have reduced hysteresis, better rollingresistance, snow and ice traction, and wet traction, and improved fueleconomy for vehicles equipped with such tires. Traditionally, improveddispersion of reinforcing fillers has been accomplished by lengthenedmixing times. However, in commercial applications, prolonged mixingtimes result in decreased production and increased expense.

With the increasing use of silica as a reinforcing filler for rubber,filler dispersion in rubber stocks has become a major concern. Becausepolar silanol groups on the surface of silica particles tend toself-associate, reagglomeration of silica particles occurs aftercompounding, leading to poor silica dispersion, a high compoundviscosity and a shorter scorch time. Therefore, it is desirable toimprove the dispersion of silica in rubber compounds, especially whenused for tire treads, to improve performance characteristics.

Previous attempts at preparing readily processable, vulcanizablesilica-filled rubber stocks containing natural rubber or diene polymerand copolymer elastomers have focused on the use, during compounding, ofbifunctional silica coupling agents having a moiety (e.g., a silylgroup) reactive with the silica surface, and a moiety (e.g., a mercapto,amino, vinyl, epoxy or sulfur group) that binds to the elastomer. Wellknown examples of such silica coupling agents are mercaptosilanes andbis-(3-trialkoxysilylorgano) polysulfides, such asbis-(3-triethyoxysilylpropyl) tetrasulfide which is known commerciallyas Si69. With the coupling agent acting as an intermediary, the compoundviscosity is reduced and the silica particles are more easily dispersedinto the elastomeric matrix. However, such silica coupling agents areexpensive. In addition, the reaction of the alkoxy portion of thecoupling agent with the rubber can result in the release of asubstantial amount of alcohol, resulting in a rubber compound containingundesirable bubbles that may form blisters or surface defects in theresulting formed rubber articles.

To address the expense and other problems related to bifunctional silicacoupling agents, recent approaches to providing improved dispersion ofsilica in rubber compounds have been directed to reducing or replacingthe use of such silica coupling agents by employing dispersing agents,such as monofunctional silica shielding agents (e.g., silicahydrophobating agents that chemically react with the surface silanolgroups on the silica particles but are not reactive with the elastomer)and agents which physically shield the silanol groups, to preventreagglomeration of the silica particles after compounding. For example,dispersing agents, such as alkyl alkoxysilanes, glycols (e.g.,diethylene glycol or polyethylene glycol), fatty acid esters ofhydrogenated and non-hydrogenated C₅ and C₆ sugars (e.g., sorbitanoleates, and the like), polyoxyethylene derivatives of the fatty acidesters, and fillers such as mica, talc, urea, clay, sodium sulfate, andthe like, are the subjects of our, co-owned U.S. patent applicationsSer. Nos. 08/893,864; 08/893,875; 08/985,859; and 09/203,438. Suchsilica dispersing agents can be used to replace all or part of expensivebifunctional silica coupling agents, while improving the processabilityof silica-filled rubber compounds by reducing the compound viscosity,increasing the scorch time, and reducing silica reagglomeration. The useof such dispersing aids includes employing an increased amount ofsulfur, to replace sulfur that otherwise would have been supplied by asulfur-containing silica coupling agent, in order to achieve asatisfactory cure of the rubber compound.

Although the above-described silica dispersing agents provide goodsilica dispersion in vulcanizable elastomeric compounds, there is stilla need for other silica dispersing agents that can be similarly used.

SUMMARY OF THE INVENTION

The present invention provides a processing aid for improving thedispersion of silica in a sulfur-vulcanizable elastomeric compositionwhile eliminating or reducing the use of a bifunctional silica couplingagent. In particular, the processing aid of the invention comprises oneor more amide compounds, selected from the group of amide compoundshaving the formula

wherein R is selected from the group consisting of primary, secondaryand tertiary alkyl groups having 1 to about 30 carbon atoms, alkarylgroups having about 5 to about 30 carbon atoms, and cycloaliphaticgroups having about 5 to about 30 carbon atoms; R′ and R″ are the sameor different from each other and are selected from the group consistingof hydrogen, C₁ to about C₃₀ aliphatic, and about C₅ to about C₃₀cycloaliphatic; R and R′ may be linked together to form a ringstructure; and R′ and R″ may be linked together to form a ringstructure.

As defined herein, the amide compound suitable for use as a processingaid in the vulcanizable elastomeric compositions of the invention has apolar end that is weakly chemically reactive with the polar groups onsilica particles, such as by hydrogen bonding and the like, and anon-polar end that is weakly chemically reactive with the elastomer,such as by hydrogen bonding, van der Waals forces, and the like. Theterms “processing aid” and “dispersing aid” are used interchangeablyherein to refer to the dispersion of reinforcing filler, especiallysilica, in the compositions.

Exemplary amide compounds for use as processing aids in the inventioncompositions include, but are not limited to, erucamide, octadecanamide,ε-caprolactam, N,N-diethyldodecanamide, and N,N-diethyl-m-toluamide.Mixtures of amide compounds may also be employed.

The present invention provides a vulcanizable elastomeric compositioncomprising an elastomer, a reinforcing filler comprising silica or amixture thereof with carbon black, a processing aid comprising an amidecompound as described above, at least one cure agent, and a sufficientamount of sulfur to achieve a satisfactory cure of the composition. Theamide compound is present in an amount of about 0.1% to about 150% byweight based on the weight of the silica. Preferably, the amide compoundis present in an amount of about 0.5% to about 50% by weight and, morepreferably, in the amount of about 1% to about 30% by weight based onthe weight of the silica.

In another embodiment, the invention provides a process for thepreparation of a vulcanized elastomeric composition comprising the stepsof a) mixing an elastomer with a reinforcing filler comprising silica ora mixture thereof with carbon black, a processing aid comprising anamide compound as described above, at least one cure agent, and asufficient amount of sulfur to achieve a satisfactory cure of thecomposition; and b) effecting vulcanization.

The use of an amide compound as a processing aid results in a reductionof the compound Mooney viscosity to a level that is comparable to acomposition employing a polysulfide silica coupling agent, such as Si69and the like; and provides a longer processing time window during theextrusion process to facilitate filling of the tire mold during cure.Moreover, the use of an amide compound as a processing aid results in animproved scorch time, reduced silica flocculation, lower silica networkbuildup, improved mold flow control of filler morphologies in the greenstate, and improved cure rate. These properties, in vulcanized articlesutilizing the present invention, are indicative of improved hysteresiswhich, in turn, results in equivalent or better rolling resistance, wet,ice and snow traction, and improved fuel economy for vehicles equippedwith such tires.

In another embodiment of the invention, the vulcanizable elastomericcomposition further comprises, in addition to the amide compound, anadditional processing aid, such as an alkyl alkoxysilane, a fatty acidester of hydrogenated or non-hydrogenated C₅ and C₆ sugars, thepolyoxyethylene derivatives thereof, or a mineral or non-mineraladditional filler, such as mica, talc, clay, aluminum hydrate, urea,sodium sulfate, and the like. For example, the addition of anotherprocessing aid, such as an alkyl alkoxysilane, to the compositioncontaining the amide compound results in a further reduction in thecompound Mooney viscosity, improved silica flocculation stability aftercompounding, and improved scorch time and cure rate.

The invention further provides a pneumatic tire comprising at least onecomponent produced from the vulcanized elastomeric compositioncontaining the amide compound processing aid.

DETAILED DESCRIPTION OF THE INVENTION

It has been discovered that the use of an amide compound as a dispersingaid for silica filler in a vulcanizable elastomeric composition, in theabsence of other silica coupling agents or silica shielding agents,improves the processability of the rubber compositions by, for example,reducing the compound viscosity and increasing the scorch time, comparedto silica-filled elastomeric compositions not containing the processingaid. Moreover, it has been discovered that rubber compositions processedusing an amide compound as a processing aid, in the absence of othersilica coupling agents or silica shielding agents, surprisingly possessfavorable viscoelastic properties. These improved properties include alower elastic modulus (G′) at −20° C., a higher tan δ at 0° C., and alower tan δ at 50° C. Such properties have been commonly used in thetire industry to predict tire performance in the categories of snow andice traction (G′ at −20° C.), wet traction (tan δ at 0° C.), and rollingresistance (tan δ at 50° C.). Rubber stocks containing amide compoundsas filler dispersing aids also exhibit a reduced Payne effect (i.e., alower silica network build-up after compounding) and improved fillerdispersion, which will result in lower hysteresis in the vulcanizedproduct.

The processing aid in the invention vulcanizable elastomeric compositioncomprises an amide compound selected from a group of amide compoundshaving the formula

where R is selected from the group consisting of primary, secondary andtertiary alkyl groups having 1 to about 30 carbon atoms, alkaryl groupshaving about 5 to about 30 carbon atoms, and cycloaliphatic groupshaving about 5 to about 30 carbon atoms; R′ and R″ are the same ordifferent from each other and are selected from the group consisting ofhydrogen, C₁ to about C₃₀ aliphatic, and about C₅ to about C₃₀cycloaliphatic; R and R′ may be linked together to form a ringstructure; and R′ and R″ may be linked together to form a ringstructure.

As illustrated by the foregoing formula, the amide compound has a polar“head” comprising a nitrogen atom and a carbonyl group, and a non-polarlipophilic alkyl “tail.” It is believed that the polar head of the amidecompound is attracted to the hydrophilic surface of the silica fillerand bonds to the silica by hydrogen bonding. The lipophilic alkyl tailof the amide compound is compatible with the elastomeric material andassociates with the elastomer through weak bonding, such as hydrogenbonding, van der Waals forces, and the like. Without being bound bytheory, it is believed that during compounding, the amide compound mayposition itself between silica particles in the silica aggregates, andprevent or reduce agglomeration of the aggregates. Thus, theagglomerates of silica particles, once held together by the attractionbetween their hydrophilic surfaces, are reduced in size due to thepresence of the amide compound during and after compounding. The amidecompound suitable as a filler dispersing aid is not in polymeric form.

Exemplary amide compounds for use as processing aids in the compositionsof the invention include, but are not limited to, erucamide,octadecanamide, ε-caprolactam, N,N-diethyldodecanamide, andN,N-diethyl-m-toluamide. Mixtures of amide compounds may also beemployed.

The amide compound is present in the vulcanizable elastomericcomposition in an amount of about 0.1% to about 150% by weight based onthe weight of the silica. Preferably the amide compound is present in anamount of about 0.5% to about 50% by weight and, more preferably, in theamount of about 1% to about 30% by weight based on the weight of thesilica.

The amide compound processing aid may be added separately to theelastomer or may be fully or partially supported on the reinforcingfiller. The ratio of the amide compound to the reinforcing filler is notcritical. If the amide compound is a liquid, a suitable ratio of amidecompound to filler is that which results in a suitably dry material foraddition to the elastomer. For example, the ratio may be about 1/99 toabout 70/30, about 20/80 about 60/40, about 50/50, and the like.

The amide compound processing aid of the invention may be used as asilica dispersing aid to replace all or at least a portion of abifunctional silica coupling agent in a sulfur-vulcanizable elastomericcompositions. However, it has been found herein that when asulfur-containing silica coupling agent is absent or reduced inconcentration, an appropriate adjustment in the amount of sulfur addedto the elastomeric composition is necessary to achieve a satisfactorycure of the composition. For example, an effective amount of sulfur inan invention composition would provide a property of the cured compoundthat is approximately equal to the same property of a satisfactorilycured compound containing Si69 or a mercaptosilane with a conventionalamount of sulfur (e.g., about 1.4 to about 2.5 phr). Exemplary curedproperties for comparison include, but are not limited to, the value ofthe 300% Modulus (psi), the molecular weight between crosslinks (Mcg/mol), and the like, and other cured properties that are well known tothose skilled in the art of rubber making. The increased amount ofsulfur to compensate for the reduced availability of sulfur from asulfur-donating silica coupling agent will vary from composition tocomposition, depending on the amount of silica and the amount, if any,of a sulfur-donating silica coupling agent present in the formulation.Based on the disclosure contained herein, and in the examples ofinvention compositions described below, one skilled in the art of rubbercompounding may easily determine the effective amount of sulfur requiredfor a satisfactory cure of the compound without undue experimentation.The additional sulfur may take any form, including soluble sulfur,insoluble sulfur, or any of the sulfur-donating compounds described asvulcanizing agents below, or mixtures of the foregoing.

Although the amide compound may be used alone as a dispersing/processingaid in the present invention to produce vulcanizable elastomericcompositions and vulcanized rubber products exhibiting favorablephysical properties, it has also been discovered that these propertiesshow a greater improvement when the amide compound is used inconjunction with additional dispersing aids. Therefore, in anotherembodiment of the invention, the vulcanizable elastomeric compositioncomprises an additional dispersing aid, such as an alkyl alkoxysilane, afatty acid ester of hydrogenated or non-hydrogenated C₅ and C₆ sugars,and the polyoxyethylene derivatives thereof, or a mineral or non-mineraladditional filler, as described below.

Alkyl alkoxysilanes useful as an additional processing aid preferablyhave the formula

(R₁)₃—Si(OR₂) or (R₁)₂—Si(OR₂)₂ or (R₁)—Si(OR₂)₃

where the alkoxy groups are the same or are different from each other;each R₁ independently comprises a C₁ to about C₂₀ aliphatic, about C₅ toabout C₂₀ cycloaliphatic, or about C₅ to about C₂₀ aromatic group; andeach R₂ independently comprises from one to about 6 carbon atoms.Preferably, R₁ comprises a C₁ to about C₁₀ aliphatic, about C₆ to aboutC₁₀ cycloaliphatic, or about C₆ to about C₁₂ aromatic group.

Exemplary alkyl alkoxysilanes include, but are not limited to, octyltriethoxysilane, octyl trimethoxysilane, trimethyl ethoxysilane, silylethoxysilane, cyclohexyl triethoxysilane, iso-butyl triethoxysilane,ethyl trimethoxy silane, hexyl tributoxy silane, dimethyldiethoxysilane, methyl triethoxysilane, propyl triethoxysilane, hexyltriethoxysilane, heptyl triethoxysilane, nonyl triethoxysilane,octadecyl triethoxysilane, methyl octyl diethoxysilane, dimethyldimethoxysilane, methyl trimethoxysilane, propyl trimethoxysilane, hexyltrimethoxysilane, heptyl trimethoxysilane, nonyl trimethoxysilane,octadecyl trimethoxysilane, methyl octyl dimethoxysilane, and mixturesthereof. Because alcohol is released when the alkyl alkoxysilane reactswith the surface of the silica particle, it is preferred forenvironmental reasons that ethoxysilanes are employed, rather thanmethoxysilanes, although methoxysilanes are not excluded from theinvention. Preferred alkyl alkoxysilane processing aids are octyltriethoxysilane, octadecyl triethoxysilane, and nonyl triethoxysilane.

The alkyl alkoxysilane, if used, may be present in an amount of about0.1% to about 150% by weight based on the weight of the silica.Preferably, the alkyl alkoxysilane may be present in an amount of about0.5% to about 50% by weight and, more preferably, in an amount of about1% to about 30% by weight based on the weight of the silica. If desired,the alkyl alkoxysilane may be fully or partially supported by thereinforcing filler. The ratio of the alkyl alkoxysilane to thereinforcing filler is not critical. For example, the ratio may be about1/99 to about 70/30, about 20/80 about 60/40, about 50/50, and the like.The addition of the alkyl alkoxysilane processing aid to the compositionresults in a further reduction in the compound Mooney viscosity,improved silica flocculation stability, and improved scorch time andcure rate.

Exemplary fatty acid esters of hydrogenated and non-hydrogenated C₅ andC₆ sugars (e.g., sorbose, mannose, and arabinose) that are useful as anadditional processing aid include the sorbitan oleates, such as sorbitanmonooleate, dioleate, trioleate and sesquioleate, as well as sorbitanesters of laurate, palmitate and stearate fatty acids. Fatty acid estersof hydrogenated and non-hydrogenated C₅ and C₆ sugars are commerciallyavailable from ICI Specialty Chemicals (Wilmington, Del.) under thetrade name SPAN®. Representative products include SPAN® 60 (sorbitanstearate), SPAN® 80 (sorbitan oleate), and SPAN® 85 (sorbitantrioleate). Other commercially available fatty acid esters of sorbitanare also available, such as the sorbitan monooleates known as Alkamul®SMO; Capmul® O); Glycomul® O; Arlacel® 80; Emsorb® 2500; and S-Maz® 80.Generally, a useful amount of these additional processing aids is about0.1% to about 60% by weight based on the weight of the silica, withabout 0.5% to about 50% by weight being preferred, and about 1% to about30% by weight based on the weight of the silica being more preferred.Esters of polyols, including glycols such as polyhydroxy compounds andthe like, in the same quantities, are also useful.

Exemplary polyoxyethylene derivatives of fatty acid esters ofhydrogenated and non-hydrogenated C₅ and C₆ sugars include, but are notlimited to, polysorbates and polyoxyethylene sorbitan esters, which areanalogous to the fatty acid esters of hydrogenated and non-hydrogenatedsugars noted above except that ethylene oxide groups are placed on eachof the hydroxyl groups. Representative examples of polyoxyethylenederivatives of sorbitan include POE® (20) sorbitan monooleate,Polysorbate® 80, Tween® 80, Emsorb® 6900, Liposorb® O-20, T-Maz® 80, andthe like. The Tween® products are commercially available from ICISpecialty Chemicals. Generally, a useful amount of these additionalprocessing aids is about 0.1% to about 60% by weight based on the weightof the silica, with about 0.5% to about 50% by weight being preferred,and about 1% to about 30% by weight based on the weight of the silicabeing more preferred.

The fatty acid esters described above, and their polyoxyethylenederivatives, may be fully or partially supported by the reinforcingfiller. The ratio of the dispersing agent to the reinforcing filler isnot critical. If the dispersing agent is a liquid, a suitable ratio ofdispersing agent to filler is that which results in a suitably drymaterial for addition to the elastomer. For example, the ratio may beabout 1/99 to about 70/30, about 20/80 about 60/40, about 50/50, and thelike.

Certain additional fillers can be utilized according to the presentinvention as processing aids, including mineral fillers, such as clay(hydrous aluminum silicate), talc (hydrous magnesium silicate), aluminumhydrate [Al(OH)₃] and mica, as well as non-mineral fillers such as ureaand sodium sulfate. Preferred micas principally contain alumina andsilica, although other known variants are also useful. The foregoingadditional fillers are optional and can be utilized in the amount ofabout 0.5 to about 40 phr, preferably in an amount of about one to about20 phr and, more preferably in an amount of about one to about 10 phr.These additional fillers can also be used as non-reinforcing fillers tosupport the amide compound processing aids, as well as any of theoptional additional processing aids described above. As with the supportof the processing aid on the reinforcing filler, as described above, theratio of processing aid to non-reinforcing filler is not critical. Forexample, the ratio may be about 1/99 to about 70/30, about 20/80 about60/40, about 50/50, and the like.

The present invention can be used in conjunction with any anionicallypolymerized elastomer. For example, conjugated diene monomers, monovinylaromatic monomers, triene monomers, and the like, may be anionicallypolymerized to form conjugated diene polymers, or copolymers orterpolymers of conjugated diene monomers and monovinyl aromatic monomers(e.g., styrene, alpha methyl styrene and the like) and triene monomers.Thus, the elastomeric products may include diene homopolymers frommonomer A and copolymers thereof with monovinyl aromatic monomers B.Exemplary diene homopolymers are those prepared from diolefin monomershaving from about four to about 12 carbon atoms. Exemplary vinylaromatic copolymers are those prepared from monomers having from abouteight to about 20 carbon atoms. Copolymers can comprise from about 99percent to about 10 percent by weight of diene units and from about oneto about 90 percent by weight of monovinyl aromatic or triene units,totaling 100 percent. The polymers, copolymers and terpolymers of thepresent invention may have 1,2-microstructure contents ranging fromabout 10 percent to about 80 percent, with the preferred polymers,copolymers or terpolymers having 1,2-microstructure content of fromabout 25 to 65 percent, based upon the diene content. The elastomericcopolymers are preferably random copolymers which result fromsimultaneous copolymerization of the monomers A and B with randomizingagents, as is known in the art.

Preferred polymers for use in a vulcanizable elastomeric composition ofthe invention include polyisoprene, polystyrene, polybutadiene,butadiene-isoprene copolymer, butadiene-isoprene-styrene terpolymer,isoprene-styrene copolymer, and styrene-butadiene copolymer.

Anionic polymerization initiators for use in polymerizing theanionically polymerizable monomers include, but are not limited to,organo-sodium, organo-potassium, organo-tin, and organo-lithiuminitiators. As an example of such initiators, organo-lithium compoundsuseful in the polymerization of 1,3-diene monomers are hydrocarbyllithium compounds having the formula RLi, where R represents ahydrocarbyl group containing from one to about 20 carbon atoms, andpreferably from about 2 to about 8 carbon atoms. Although thehydrocarbyl group is preferably an aliphatic group, the hydrocarbylgroup can also be cycloaliphatic or aromatic. The aliphatic group may bea primary, secondary, or tertiary group, although the primary andsecondary groups are preferred. Examples of aliphatic hydrocarbyl groupsinclude methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl,n-amyl, sec-amyl, n-hexyl, sec-hexyl, n-heptyl, n-octyl, n-nonyl,n-dodecyl, and octadecyl. The aliphatic group can contain someunsaturation, such as allyl, 2-butenyl, and the like. Cycloalkyl groupsare exemplified by cyclohexyl, methylcyclohexyl, ethylcyclohexyl,cycloheptyl, cyclopentylmethyl, and methylcyclopentylethyl. Examples ofaromatic hydrocarbyl groups include phenyl, tolyl, phenylethyl, benzyl,naphthyl, phenyl cyclohexyl, and the like.

Specific examples of organo-lithium compounds which are useful asanionic initiators in the polymerization of the monomers listed above,especially conjugated dienes include, but are not limited to, n-butyllithium, n-propyl lithium, iso-butyl lithium, tert-butyl lithium,tributyl tin lithium (described in our co-owned U.S. Pat. No.5,268,439), amyl-lithium, cyclohexyl lithium, and the like. Othersuitable organo-lithium compounds for use as anionic initiators are wellknown to those skilled in the art. A mixture of different lithiuminitiator compounds also can be employed. The preferred organo-lithiuminitiators are n-butyl lithium, tributyl tin lithium and “in situ”produced lithium hexamethyleneimide initiator prepared by reactinghexamethyleneimine and n-butyl lithium (described in our co-owned U.S.Pat. No. 5,496,940).

The amount of initiator required to effect the desired polymerizationcan be varied over a wide range depending upon a number of factors, suchas the desired polymer molecular weight, the desired 1,2- and1,4-content of the polydiene, and the desired physical properties forthe polymer produced. In general, the amount of initiator utilized canvary from as little as 0.2 millimoles (mM) of lithium per 100 grams ofmonomers up to about 100 mM of lithium per 100 grams of monomers,depending upon the desired polymer molecular weight.

Polymerization is usually conducted in a conventional solvent foranionic polymerizations, such as hexane, cyclohexane, benzene and thelike. Various techniques for polymerization, such as semi-batch andcontinuous polymerization may be employed.

In order to promote randomization in co-polymerization and to increasevinyl content, a polar coordinator may optionally be added to thepolymerization ingredients. Amounts range between about one to about 90or more equivalents per equivalent of lithium. The amount depends uponthe type of polar coordinator that is employed, the amount of vinyldesired, the level of styrene employed and the temperature of thepolymerizations, as well as the selected initiator. Compounds useful aspolar coordinators are organic and include tetrahydrofuran, linear andcyclic oligomeric oxolanyl alkanes such as 2-2′-di(tetrahydrofuryl)propane, dipiperidyl ethane, hexamethyl phosphoramide, N-N′-dimethylpiperazine, diazabicyclo octane, dimethyl ether, diethyl ether, tributylamine and the like. The linear and cyclic oligomeric oxolanyl alkanepolar coordinators are described in U.S. Pat. No. 4,429,091, the subjectmatter of which regarding polar coordinators is incorporated herein byreference. Other compounds useful as polar coordinators include thosehaving an oxygen or nitrogen hetero-atom and a non-bonded pair ofelectrons. Examples include dialkyl ethers of mono and oligo alkyleneglycols; “crown” ethers; and tertiary amines, such astetramethylethylene diamine (TMEDA).

Polymerization is begun by charging a blend of the monomer(s) andsolvent to a suitable reaction vessel, followed by the addition of thepolar coordinator and the initiator previously described. The procedureis carried out under anhydrous, anaerobic conditions. Often, it isconducted under a dry, inert gas atmosphere. The polymerization can becarried out at any convenient temperature, such as about 0° C. to about150° C. For batch polymerizations, it is preferred to maintain the peaktemperature at from about 50° C. to about 150° C. and, more preferably,from about 60° C. to about 100° C. Polymerization is allowed to continueunder agitation for about 0.15 hours to 24 hours. After polymerizationis complete, the product is terminated by a quenching agent, anendcapping agent and/or a coupling agent, as described herein below. Theterminating agent is added to the reaction vessel, and the vessel isagitated for about 0.1 hours to about 4.0 hours. Quenching is usuallyconducted by stirring the polymer and quenching agent for about 0.01hours to about 1.0 hour at temperatures of from about 20° C. to about120° C. to ensure a complete reaction. Polymers terminated with afunctional group, as discussed herein below, are subsequently quenchedwith alcohol or other quenching agent as also described herein below.

Lastly, the solvent is removed from the polymer by conventionaltechniques such as drum drying, extruder drying, vacuum drying or thelike, which may be combined with coagulation with water, alcohol orsteam. If coagulation with water or steam is used, oven drying may bedesirable.

One way to terminate the polymerization reaction is to employ a proticquenching agent to give a monofunctional polymer chain. Quenching may beconducted in water, steam or an alcohol such as isopropanol, or anyother suitable method. Quenching may also be conducted with a functionalterminating agent, resulting in a difunctional polymer. Any compoundsproviding terminal functionality (i.e., endcapping) that are reactivewith the polymer bound carbon-magnesium-lithiun moiety can be selectedto provide a desired functional group. Examples of such compounds arealcohols, substituted aldimines, substituted ketimines, Michler'sketone, 1,3-dimethyl-2-imidazolidinone, 1-alkyl substitutedpyrrolidinones, 1-aryl substituted pyrrolidinones, tin tetrachloride,tributyl tin chloride, carbon dioxide, and mixtures thereof. Furtherexamples of reactive compounds include the terminators described in ourco-owned U.S. Pat. Nos. 5,521,309 and 5,066,729, the subject matter ofwhich, pertaining to terminating agents and terminating reactions, ishereby incorporated by reference. Other useful terminating agents mayinclude those of the structural formula (R)_(a) ZX_(b), where Z is tinor silicon. It is preferred that Z is tin. R is an alkyl having fromabout 1 to about 20 carbon atoms; a cycloalkyl having from about 3 toabout 20 carbon atoms; an aryl having from about 6 to about 20 carbonatoms, or an aralkyl having from about 7 to about 20 carbon atoms. Forexample, R may include methyl, ethyl, n-butyl, neophyl, phenyl,cyclohexyl or the like. X is a halogen, such as chlorine or bromine, oralkoxy (—OR), “a” is an integer from zero to 2, and “b” is an integerfrom one to 4, where a+b =4. Examples of such terminating agents includetin tetrachloride, tributyl tin chloride, butyl tin trichloride, butylsilicon trichloride, as well as tetraethoxysilane (Si(OEt)₄), and methyltriphenoxysilane (MeSi(OPh)₃). The practice of the present invention isnot limited solely to these terminators, since other compounds that arereactive with the polymer bound carbon-lithium moiety can be selected toprovide a desired functional group.

While terminating to provide a functional group on the terminal end ofthe polymer is preferred, it is furither preferred to terminate by acoupling reaction with, for example, tin tetrachloride or other couplingagent such as silicon tetrachloride or esters. High levels of tincoupling are desirable in order to maintain good processability in thesubsequent manufacturing of rubber products. It is preferred that thepolymers for use in the vulcanizable elastomeric compositions accordingto the present invention have at least about 40 percent tin coupling.That is, about 40 percent of the polymer mass after coupling is ofhigher molecular weight than the polymer before coupling as measured,for example, by gel permeation chromatography. Preferably, beforecoupling, the polydispersity (the ratio of the weight average molecularweight to the number average molecular weight) of polymers, which can becontrolled over a wide range, is from about one to about 5, preferablyone to about 2 and, more preferably, one to about 1.5.

As noted above, various techniques known in the art for carrying outpolymerizations may be used to produce elastomers polymers suitable foruse in the vulcanizable elastomeric compositions, without departing fromthe scope of the present invention.

Vulcanizable elastomeric compositions of the invention are prepared bymixing an elastomer with silica, or a mixture of silica and carbonblack, and an amide compound processing aid, preferably with theaddition of at least one additional processing aid such as alkylalkoxysilanes, fatty acid esters or their polyoxyethylene derivatives,as described above, or polyol esters, in addition to other conventionalrubber additives including, for example, other fillers, plasticizers,antioxidants, cure agents and the like, using standard rubber mixingequipment and procedures. Such elastomeric compositions, when vulcanizedusing conventional rubber vulcanization conditions, exhibit reducedhysteresis, which means a product having increased rebound, decreasedrolling resistance and lessened heat build-up when subjected tomechanical stress. Products including tires, power belts and the likeare envisioned. Decreased rolling resistance is, of course, a usefulproperty for pneumatic tires, both radial as well as bias ply types andthus, the vulcanizable elastomeric compositions of the present inventioncan be utilized to form treadstocks for such tires. Pneumatic tires canbe made according to the constructions disclosed in U.S. Pat. Nos.5,866,171; 5,876,527; 5,931,211; and 5,971,046, the disclosures of whichare incorporated herein by reference. The composition can also be usedto form other elastomeric tire components such as subtreads, blacksidewalls, body ply skims, bead fillers and the like.

The preferred conjugated diene polymers, or copolymers or terpolymers ofconjugated diene monomers and monovinyl aromatic monomers, can beutilized as 100 parts of the rubber in the treadstock compound, or theycan be blended with any conventionally employed treadstock rubber whichincludes natural rubber, synthetic rubber and blends thereof. Suchrubbers are well known to those skilled in the art and include syntheticpolyisoprene rubber, styrene-butadiene rubber (SBR), polybutadiene,butyl rubber, neoprene, ethylene-propylene rubber,ethylene-propylene-diene rubber (EPDM), acrylonitrile-butadiene rubber(NBR), silicone rubber, the fluoroelastomers, ethylene acrylic rubber,ethylene vinyl acetate copolymer (EVA), epichlorohydrin rubbers,chlorinated polyethylene rubbers, chlorosulfonated polyethylene rubbers,hydrogenated nitrile rubber, tetrafluoroethylene-propylene rubber andthe like. When the vulcanizable elastomeric composition of the presentinvention is blended with conventional rubbers, the amounts can varywidely with a lower limit comprising about ten percent to 20 percent byweight of the total rubber. The minimum amount will depend primarilyupon the physical properties desired.

The vulcanizable elastomeric composition is preferably compounded withreinforcing fillers, such as silica, or a mixture of silica and carbonblack. Examples of silica fillers which may be used in the vulcanizableelastomeric composition of the invention include wet silica (hydratedsilicic acid), dry silica (anhydrous silicic acid), calcium silicate,and the like. Other suitable fillers include aluminum silicate,magnesium silicate, and the like. Among these, precipitated amorphouswet-process, hydrated silicas are preferred. These silicas are so-calledbecause they are produced by a chemical reaction in water, from whichthey are precipitated as ultrafine, spherical particles. These primaryparticles strongly associate into aggregates, which in turn combine lessstrongly into agglomerates. The surface area, as measured by the BETmethod gives the best measure of the reinforcing character of differentsilicas. For silicas of interest for the present invention, the surfacearea should be about 32 m²/g to about 400 m²/g, with the range of about100 m²/g to about 250 m²/g being preferred, and the range of about 150m²/g to about 220 m²/g being most preferred. The pH of the silica filleris generally about 5.5 to about 7 or slightly over, preferably about 5.5to about 6.8.

Silica can be employed in the amount of about one to about 100 parts perhundred parts of the elastomer, preferably in an amount of about five toabout 80 phr and, more preferably, in an amount of about 30 to about 80phr. The useful upper range is limited by the high viscosity imparted byfillers of this type. Some of the commercially available silicas whichmay be used include, but are not limited to, Hi-Sil® 190, Hi-Sil® 210,Hi-Sil® 215, Hi-Sil® 233, Hi-Sil® 243, and the like, produced by PPGIndustries (Pittsburgh, Pa.). A number of useful commercial grades ofdifferent silicas are also available from DeGussa Corporation (e.g.,VN2, VN3), Rhone Poulenc (e.g., Zeosil® 1165MP), and J.M. HuberCorporation.

The elastomers can be compounded with all forms of carbon black in amixture with the silica. The carbon black may be present in amountsranging from about one to about 50 phr, with about five to about 35 phrbeing preferred. The carbon blacks may include any of the commonlyavailable, commercially-produced carbon blacks, but those having asurface area (EMSA) of at least 20 m²/g and, more preferably, at least35 m²/g up to 200 m²/g or higher are preferred. Surface area values usedin this application are determined by ASTM D-1765 using thecetyltrimethyl-ammonium bromide (CTAB) technique. Among the usefulcarbon blacks are furnace black, channel blacks and lamp blacks. Morespecifically, examples of useful carbon blacks include super abrasionfurnace (SAF) blacks, high abrasion furnace (HAF) blacks, fast extrusionfurnace (FEF) blacks, fine furnace (FF) blacks, intermediate superabrasion furnace (ISAF) blacks, semi-reinforcing furnace (SRF) blacks,medium processing channel blacks, hard processing channel blacks andconducting channel blacks. Other carbon blacks which may be utilizedinclude acetylene blacks. A mixture of two or more of the above blackscan be used in preparing the carbon black products of the invention.Typical suitable carbon blacks are N-110, N-220, N-339, N-330, N-351,N-550, N-660, as designated by ASTM D-1765-82a. The carbon blacksutilized in the preparation of the vulcanizable elastomeric compositionsof the invention may be in pelletized form or an unpelletized flocculentmass. Preferably, for more uniform mixing, unpelletized carbon black ispreferred.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various vulcanizablepolymer(s) with various commonly used additive materials such as, forexample, curing agents, activators, retarders and accelerators,processing additives, such as oils, resins, including tackifying resins,plasticizers, pigments, additional fillers, fatty acid, zinc oxide,waxes, antioxidants, anti-ozonants, and peptizing agents. As known tothose skilled in the art, depending on the intended use of the sulfurvulcanizable and sulfur vulcanized material (rubbers), the additivesmentioned above are selected and commonly used in conventional amounts.

Typical amounts of tackifier resins, if used, comprise about 0.5 toabout 10 phr, usually about one to about 5 phr. Typical amounts ofcompounding aids comprise about one to about 50 phr. Such compoundingaids can include, for example, aromatic, naphthenic, and/or paraffinicprocessing oils. Typical amounts of antioxidants comprise about 0.1 toabout 5 phr. Representative antioxidants may be, for examplediphenyl-p-phenylenediamine and others, such as for example, thosedisclosed in the Vanderbilt Rubber Handbook (1978), pages 344 to 346.Typical amounts of anti-ozonants comprise about 0.1 to about 5 phr.

Typical amounts of fatty acids, if used, which can include stearic acid,palmitic acid, linoleic acid or a mixture of one or more fatty acids,can comprise about 0.5 to about 3 phr. Typical amounts of zinc oxidecomprise about two to about 5 phr. Typical amounts of waxes compriseabout one to about 2 phr. Often microcrystalline waxes are used. Typicalamounts of peptizers, if used, comprise about 0.1 to about 1 phr.Typical peptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

The reinforced rubber compounds can be cured in a conventional mannerwith known vulcanizing agents at about 0.1 to 10 phr. For a generaldisclosure of suitable vulcanizing agents, one can refer to Kirk-Othmer,Encyclopedia of Chemical Technology, 3rd ed., Wiley Interscience, N.Y.1982, Vol. 20, pp. 365 to 468, particularly “Vulcanization Agents andAuxiliary Materials,” pp. 390 to 402. Vulcanizing agents can be usedalone or in combination.

The vulcanization is conducted in the presence of a sulfur vulcanizingagent. Examples of suitable sulfur vulcanizing agents include“rubbermaker's” soluble sulfur; sulfur donating vulcanizing agents, suchas an amine disulfide, polymeric polysulfide or sulfur olefin adducts;and insoluble polymeric sulfur. Preferably, the sulfur vulcanizing agentis soluble sulfur or a mixture of soluble and insoluble polymericsulfur. The sulfur vulcanizing agents are used in an amount ranging fromabout 0.1 to about 10 phr, more preferably about 1.5 to about 5 phr,with a range of about 1.5 to about 3.5 phr being most preferred.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve properties of the vulcanizate. Thevulcanization accelerators used in the present invention are notparticularly limited. Examples include thiazol vulcanizationaccelerators, such as 2-mercaptobenzothiazol, dibenzothiazyl disulfide,N-cyclohexyl-2-benzothiazyl-sulfenamide (CBS),N-tert-butyl-2-benzothiazyl sulfenamide (TBBS), and the like; andguanidine vulcanization accelerators, such as diphenylguanidine (DPG)and the like. The amount of the vulcanization accelerator used is about0.1 to about 5 phr, preferably about 0.2 to about 3 phr.

The vulcanizable elastomeric composition of the present invention can beobtained by milling the components by using a milling apparatus, such asa mill, an internal mixer, and the like for a sufficient time and at ahigh enough temperature to achieve the desired physical properties ofthe resulting compound. The mixing of the vulcanizable elastomericcomposition can be accomplished by methods known to those having skillin the rubber mixing art. For example, the ingredients may be mixed intwo or more stages, consisting of at least a “master batch” stage(comprising mixing of the elastomer, with at least a portion of thesilica and/or carbon black and other ingredients); and a “final stage”,in which the cure agents are typically added. There may also be a mixingstage in which the mixture is re-milled without the addition ofingredients. The amide compound processing aid may be added in any stageof the mixing process.

The mixing temperature may vary from stage to stage. However, forpurposes of the invention, the mixing of the amide compound processingaid and the silica filler may take place at a mixing temperature ofabout 60° C. to about 200° C., typically 90° C. to about 190° C. and,more preferably, about 120° C. to about 180° C. In one embodiment of theinvention, a portion of the silica and/or amide compound processing aid,or additional dispersing aids, may be added to the master batch stage,and the remainder added to a remill stage.

EXAMPLES

The following examples illustrate methods of preparation of thevulcanizable elastomeric composition of the present invention. However,the examples are not intended to be limiting, as other methods forpreparing these compositions and different compounding formulations maybe determined by those skilled in the art. Thus, the invention is notlimited to the specific elastomers, amide compounds or additionalprocessing aids, silica, or other compound ingredients disclosed, nor toany particular amount of an ingredient in the composition. Moreover, theinvention is not limited to the mixing times or temperatures, or to thestage in which the particular ingredients are added to the mixer. Theexamples have been provided merely to demonstrate the practice of thesubject invention and do not constitute limitations of the invention.Those skilled in the art may readily select other elastomers, amidecompounds, alkyl alkoxysilanes, additional dispersing aids, silicacoupling agents, and the like, and process conditions, according to thedisclosure made hereinabove. Thus, it is believed that any of thevariables disclosed herein can readily be determined and controlledwithout departing from the scope of the invention herein disclosed anddescribed.

Example 1

In order to demonstrate the preparation and properties of thevulcanizable elastomeric compositions of the present invention sevenstocks of rubbers were prepared using the formulation and mixingconditions shown in Table 1 and Table 2. Each of five stocks wereprepared in which an amide compound processing aid was added to theelastomer/silicalcarbon black composition, as illustrated in Table 3.These stocks are labeled Examples 1, 2, 3, 4, and 5, and contain 3 phrof erucamide, octadecanamide, ε-monocaprolactam, N,N-diethyl-m-toluamideand, N,N-diethyldodecanamide, respectively. One stock was compoundedwithout adding any dispersing aids or silanes and was labeled Control Aas seen in Table 3. To compare the amide compound stock performance witha commonly used polysulfide silica coupling agent containing stock, 3phr of Si69 was added to a stock and labeled Control B in Table 3. Thetotal sulfur content of each other stock was adjusted to compensate forthe additional sulfur donated from the polysulfide silica coupling agentin Control B. The final stocks were sheeted and then were subsequentlymolded at 171° C. for 15 minutes.

The amide compounds, such as erucamide, octadecanamide,ε-monocaprolactam, N,N-diethyldodecanamide, and N,N-diethyl-m-toluamidewere purchased from Sigma-Aldrich Corporation (Milwaukee, Wis.) and wereused without further purification. As noted above, various techniquesknown in the art for carrying out compounding and cure with theprocessing aid of the present invention may be used without departingfrom the spirit and scope of the present invention. The examples areillustrative only and should not be construed as limiting in any way.The claims will serve to define the scope of the invention.

TABLE 1 Formulations of Stock Rubbers Ingredient Amount (phr) NaturalRubber 25.00 Solution SBR 75.00 Carbon Black (SAF) 32.00 PrecipitatedSilica 30.00 Naphthenic Process Oil 15.00 Wax 1.5 Antioxidant  0.95Sulfur varied Accelerator  1.50 Zinc Oxide 2.5 Diphenyl Guanidine 0.5

TABLE 2 Mixing Conditions Mixer 310 g Brabender Agitation Speed 60 rpmMaster Batch Stage Initial Temperature 100° C. 0 seconds chargingpolymers 30 seconds charging carbon black, silica, amide compound, alkylalkoxysilanes and/or other processing aids (if used), and all pigments 5minutes drop Drop Temperature 175° C. Remill 1- Batch Stage InitialTemperature 70° C. 0 seconds charging remilled stock 30 seconds chargingSi69 (if added) Drop Temperature 155° C. Final Batch Stage InitialTemperature 90° C. 0 seconds charging remilled stock 30 seconds chargingcure agent and accelerators Drop Temperature 105° C.

TABLE 3 Stocks with various shielding agents and silane N,N-diethylEruc- Octadeca- ε-mono N,N-diethyl- dodecan Stock Si69 amide n-amidecaprolactam m-toluamide amide Sulfur Number (phr) (phr) (phr) (phr)(phr) (phr) (phr) Control A 0 0 0 0 0 0 2.37 Control B 3 0 0 0 0 0 1.70Example 1 0 3 0 0 0 0 2.37 Example 2 0 0 3 0 0 0 2.37 Example 3 0 0 0 30 0 2.37 Example 4 0 0 0 0 3 0 2.37 Example 5 0 0 0 0 0 3 2.37

The green stock (i.e., the stock obtained after the remill stage, priorto adding the curatives) Mooney viscosity, Payne effect and curecharacteristics are shown in Table 4. The Mooney viscosity measurementwas conducted at 130° C. using a large rotor. The Mooney viscosity wasrecorded as the torque when the rotor had rotated for 4 minutes. Thesample was preheated at 130° C. for one minute before the rotor wasstarted. The Payne effects of the green stocks (the controls andexamples) were measured using the Rubber Process Analyzer (RPA) 2000viscometer (Alpha Technologies). The strain sweep experiment wasconducted at 50° C. at 6 cycles per minute (cpm) using strain sweepingfrom 0.25% to 1000%.

The t₅ was the time required to increase 5 Mooney units during aMooney-scorch measurement. The t₅ was used as an index to predict howfast a compound viscosity will rise during processing (e.g., extrusionprocessing). The t_(S2) and t₉₀ were the time when the torque rises to2% and 90%, respectively, of the total torque increase during the curecharacterization experiment. The t_(S2) and t₉₀ values were used topredict the speed of the viscosity build-up (t_(S2)) and the cure rate(t₉₀) during the cure process.

Table 4 shows that with the addition of the processing aid comprising anamide compound (Examples 1 through 5) the compound Mooney viscosity wasreduced. However, the values are still 15 to 20 Mooney units higher thanthe polysulfide silica coupling agent stock (Control B). The t₅ of thesestocks are longer than the Control A and comparable to the polysulfidesilica coupling agent stock (Control B). This gives the stocks a greatadvantage in that they have a larger processing time window, especiallyduring the extrusion process. In contrast, a high Mooney viscosity maycause subsequent problems during the cure stage, for example,difficulties in filling the tire mold during the cure step, and mayresult in modulated inner belts in the tires. When compared to Control Aand Control B, the longer t_(S2) in Examples 1 through 5, gave the stocktime to flow and to better fill the mold. Additionally, the relativelyfast cure rate (t₉₀) of the amide compound processing aid stocks(Examples 1 through 5) was greatly beneficial.

TABLE 4 The green stock Mooney and Cure Characteristics ΔG′ (G′ @ t₅0.25%- Scorch @ G′ @ t_(S2) @ t₉₀ Stock Mooney @ 130° C. 1000%) 171° C.171° C. Number 130° C. (min) (kPa) (min) (min) Control A 85.5 10.12 13641.35 11.08 Control B 56.0 18.73 794 2.19 7.14 Example 1 73.8 16.67 10981.79 8.71 Example 2 74.9 17.28 1385 1.89 8.29 Example 3 74.4 17.27 14151.92 8.46 Example 4 83.3 14.15 1441 1.61 9.12 Example 5 83.9 13.73 15181.56 8.00

The dynamic viscoelastic properties of the Examples 1 through 5 and theControls A and B are listed in Table 5 where the elastic modulus (G′) at−20° C., tan δ at 0° C. and 50° C. were obtained from temperature sweepexperiments. Temperature sweep experiments were conducted with afrequency of 31.4 radians per second (rad/sec) using 0.5% strain fortemperatures ranging from −100° C. to −10° C., and 2% strain fortemperatures ranging from −10° C. to 100° C. The Payne effect (ΔG′) andtan δ at 7% strain were obtained from the strain sweep experiment. Afrequency of 3.14 rad/sec was used for strain sweep which was conductedat 65° C. with strain sweeping from 0.25% to 14.75%.

Examples 1 through 5 showed an increase in the tan δ at 0° C., and areduction in the tan δ at 50° C. compared to Control A. The improvementin these values was completely unexpected, and will result in improvedwet traction and rolling resistance. The tan δ at 50° C. of Examples 1through 5 are higher than Control B. It was therefore desirable todecrease the tan δ at 50° C. while maintaining any favorable properties.

TABLE 5 The Viscoelastic Properties Measured by Temperature and StrainSweeps ΔG′ (MPa) @ G′ @ 65° C. tan δ @ Stock −20° C. tan δ @ tan δ @ (G′@ 0.25%- 7% Strain @ Number (MPa) 0° C. 50° C. G′ @ 14.75%) 65° C.Control A 50.3 0.2825 0.1844 2.32 0.1376 Control B 39.0 0.3308 0.17371.36 0.1018 Example 1 46.5 0.2870 0.1771 3.19 0.1457 Example 2 51.70.2909 0.1786 3.17 0.1528 Example 3 64.25 0.3393 0.1863 3.76 0.1499Example 4 44.26 0.3042 0.1817 3.82 0.1537 Example 5 50.98 0.3148 0.18443.00 0.1433

The tensile mechanical properties were measured using the standardprocedure described in the ASTM D-412 at 25° C. and are shown in Table6. The tensile test specimens were round rings with a dimension of 0.127centimeters (cm) (0.05 inches) in width and 0.191 cm (0.075 inches) inthickness. A specific gauge length of 2.54 cm (1 inch) was used for thetensile test. The amide compound processing aid containing stocks(Examples 1 through 5) showed inferior tensile mechanical propertieswhen compared to the controls (Controls A and B). The lower elasticmodulus of Examples 1 through 5 suggests a lower crosslink density whichwould lead to the lower mechanical strength and toughness. This can becorrected by an increase in the amount of sulfur provided for the cure.

TABLE 6 Tensile Mechanical Properties at 25° C. Strength, ElongationStock M50 M300 Tb at break, Eb Toughness Number (psi) (psi) (psi) (%)(psi) Control A 206 1435 2480 442 4641 Control B 250 2232 2924 369 4630Example 1 200 1338 1869 376 2984 Example 2 211 1380 1937 379 3136Example 3 234 1900 2143 328 3006 Example 4 195 1424 1955 374 3131Example 5 217 1582 2184 380 3559

Example 2

In order to further reduce the compound Mooney, Payne effect (ΔG′), andG′ at −20° C. in Examples 1 through 5, octyl triethoxysilane was addedto the amide compound containing stocks. Examples 6, 7, 8, 9, and 10were compounded with the octyl triethoxysilane and an amide compound.Controls C and D were tested to provide data regarding the effect ofadding no processing aid at all (Control C) and adding a polysulfidesilica coupling agent (Control D). Another control was added with 1.04phr of octyl triethoxysilane but no other processing aid (Control E) toillustrate the properties of a stock compounded with an alkylalkoxysilane alone.

TABLE 7 Stocks with various processing aids and silanes OctylN,N-diethyl triethoxy Eruc- Octadeca- ε-mono N,N-diethyl- dodecan StockSi69 silane amide n-amide caprolactam m-toluamide amide Sulfur Number(phr) (phr) (phr) (phr) (phr) (phr) (phr) (phr) Control C 0 0 0 0 0 0 02.37 Control D 3 0 0 0 0 0 0 1.70 Control E 0 1.04 0 0 0 0 0 2.37Example 6 0 1.04 3 0 0 0 0 2.37 Example 7 0 1.04 0 3 0 0 0 2.37 Example8 0 1.04 0 0 3 0 0 2.37 Example 9 0 1.04 0 0 0 3 0 2.37 Example 10 01.04 0 0 0 0 3 2.37

The compound Mooney and cure characteristics of Controls C through E andExamples 6 through 10 are shown in Table 8. The addition of an alkylalkoxysilane to Examples 6 through 10 show that the compound Mooney andPayne effect are reduced to a level comparable to that of thepolysulfide silica coupling agent stock (Control D). The scorch (t₅,t_(S2)) and cure time (t₉₀) of Examples 6 through 10 are longer for thescorch and shorter for the cure time than Controls C through E. Examples6 through 10 show improved processability, cure characteristics, andreduced silica flocculation compared to Controls C through E.

TABLE 8 The Green Stock Mooney and Cure Characteristics ΔG′ (kPa) @ 65°C. t₅ (G′ @ Scorch @ 0.25%- t_(S2) @ t₉₀ Stock Mooney @ 130° C. G′ @171° C. 171° C. Number 130° C. (min) 1000%) (min) (min) Control C 81.211.03 1651 1.23 9.37 Control D 57.4 18.70 928 2.25 7.21 Control E 65.816.65 1146 1.90 7.95 Example 6 56.1 22.53 794 2.37 6.79 Example 7 51.323.62 975 2.54 5.96 Example 8 60.3 20.01 1196 2.24 5.91 Example 9 62.320.30 985 2.13 8.34 Example 10 64.1 19.53 1109 2.09 7.44

Processing aids used as shielding agents should be able to disperse thesilica filler during a mixing stage and stabilize the particles duringstorage and the cure process. To examine the capability of a processingaid to stabilize silica filler morphology the Payne effect data ofExamples 6 through 10 was analyzed and compared to Controls C, D, and E.The Payne effect data was obtained from the remill stocks before andafter annealing at 171° C. for 15 minutes. The annealing conditionsemployed are similar to conventional curing conditions. The change inthe ΔG′ values were compared (i.e., Δ(ΔG′)). Of note is that thesestocks, except Control D, do not contain sulfur and curing agents,therefore the G′ increase cannot be attributed to sulfur crosslinking inExamples 6 through 10 and Controls C and E. These values indicate thedegree to which the filler flocculates prior to cure. A lower valueindicates a lower amount of filler flocculation prior to cure. Theresults are shown in Table 9. The change in the A G′ values of Examples6 through 10 are lower than Controls C through E. This shows that withthe use of alkyl alkoxysilanes and a processing aid comprising an amidecompound, it is possible to control and stabilize filler morphology inboth the green rubber stock and cured rubber.

TABLE 9 The Δ G′ of the remill stock before and after annealing at 171°C. for 15 minutes Stock Δ G′ before Δ G′ after Change in Δ G′, Numberannealing (kpa) annealing (kpa) after - before, (kpa) Control C 19364579 2823 Control D  964 2829 1865 Control E 1325 2811 1486 Example 61021 1956  935 Example 7 1098 1726  628 Example 8 1195 2589 1394 Example9 1156 2281 1125 Example 10 1232 2569 1337

The dynamic viscoelastic properties are listed in Table 10 where the G′at −20° C. and ΔG′ of Examples 6 through 10 are greatly improvedcompared to Controls C through E. This indicates an improvement in thesilica flocculation and the snow and ice traction capabilities of therubber. The tan δ values at 0° C. are higher compared with all of thecontrol stocks (Controls C through E). Additionally, the improvement inwet traction and reduced hysteresis shown in Examples 1 through 5 isretained.

TABLE 10 The Viscoelastic Properties measured by Temperatures and StrainSweeps ΔG′ (MPa) @ G′ @ 65° C. tan δ @ Stock −20° C. tan δ @ tan δ @ (G′@ 0.25%- 7% Strain @ Number (MPa) 0° C. 50° C. G′ @ 14.75%) 65° C.Control C 40.4 0.2861 0.1806 3.255 0.1448 Control D 31.1 0.3074 0.15821.625 0.1232 Control E 37.8 0.3060 0.1788 2.617 0.1373 Example 6 35.00.3155 0.1845 1.563 0.1106 Example 7 40.5 0.3316 0.1921 1.513 0.1122Example 8 36.8 0.3337 0.1895 2.792 0.1459 Example 9 28.9 0.2928 0.18852.391 0.1393 Example 36.1 0.3091 0.1871 2.549 0.1196 10

The addition of octyl triethoxysilane, with the amide compounds, inExamples 6 through 10 greatly improved the tensile mechanical propertiesof the vulcanizate. As seen in Table 11, the properties are comparableto the polysulfide silica coupling agent containing stock (Control D).

TABLE 11 Tensile Mechanical Properties at 25° C. Strength, ElongationStock M50 M300 Tb at Break, Eb Toughness Number (psi) (psi) (psi) (%)(psi) Control C 218 1744 2379 377 3831 Control D 200 1959 2720 382 4349Control E 180 1500 2324 400 3850 Example 6 162 1280 2400 452 4377Example 7 168 1341 2273 424 3942 Example 8 168 1480 1988 367 3095Example 9 160 1281 2195 430 3861 Example 172 1441 2340 417 4001 10

While the invention has been described herein with reference to thepreferred embodiments, it is to be understood that it is not intended tolimit the invention to the specific forms disclosed. On the contrary, itis intended to cover all modifications and alternative forms fallingwithin the spirit and scope of the invention.

We claim:
 1. A vulcanizable elastomeric composition comprising: anelastomer; a reinforcing filler comprising silica or a mixture thereofwith carbon black; a processing aid comprising an amide compound havinga polar end that is weakly chemically reactive with the silica and anon-polar end that is weakly chemically reactive with the elastomer; acure agent; and an effective amount of sulfur to achieve a satisfactorycure of the composition.
 2. The composition of claim 1, wherein theamide compound is selected from the group consisting of amide compoundshaving the formula

wherein R is selected from the group consisting of primary, secondaryand tertiary alkyl groups having 1 to about 30 carbon atoms, alkarylgroups having about 5 to about 30 carbon atoms, and cycloaliphaticgroups having about 5 to about 30 carbon atoms; R′ and R″ are the sameor different from each other and are selected from the group consistingof hydrogen, C₁ to about C₃₀ aliphatic, and about C₅ to about C₃₀cycloaliphatic; R and R′ may be linked together to form a ringstructure; and R′ and R″ may be linked together to form a ringstructure.
 3. The composition of claim 2, wherein the amide compound isselected from the group consisting of erucamide, octadecanamide,ε-caprolactam, N,N-diethyl dodecanamide, N,N-diethyl-m-toluamide, andmixtures thereof.
 4. The composition of claim 1, wherein the amidecompound is present in an amount of about 0.1% to about 150% by weightbased on the weight of the silica.
 5. The composition of claim 1,wherein the amide compound is fully or partially supported on thereinforcing filler.
 6. The composition of claim 1, wherein thecomposition further comprises an alkyl alkoxysilane having the formula(R₁)₃—Si(OR₂) or (R₁)₂—Si(OR₂)₂ or (R₁)—Si(OR₂)₃ wherein the alkoxygroups are the same or are different from each other; each R₁independently comprises a C₁ to about C₂₀ aliphatic, about C₅ to aboutC₂₀ cycloaliphatic, or about C₅ to about C₂₀ aromatic group; and each R₂independently comprises from one to about 6 carbon atoms.
 7. Thecomposition of claim 6, wherein the alkyl alkoxysilane is selected fromthe group consisting of octyl triethoxysilane, octyl trimethoxysilane,trimethyl ethoxysilane, silyl ethoxysilane, cyclohexyl triethoxysilane,iso-butyl triethoxysilane, ethyl trimethoxy silane, hexyl tributoxysilane, dimethyl diethoxysilane, methyl triethoxysilane, propyltriethoxysilane, hexyl triethoxysilane, heptyl triethoxysilane, nonyltriethoxysilane, octadecyl triethoxysilane, methyl octyl diethoxysilane,dimethyl dimethoxysilane, methyl trimethoxysilane, propyltrimethoxysilane, hexyl trimethoxysilane, heptyl trimethoxysilane, nonyltrimethoxysilane, octadecyl trimethoxysilane, methyl octyldimethoxysilane, and mixtures thereof.
 8. The composition of claim 6,wherein the alkyl alkoxysilane is present in an amount of about 0.1% toabout 150% by weight based on the weight of the silica.
 9. Thecomposition of claim 6, wherein the alkyl alkoxysilane is fully orpartially supported on the reinforcing filler.
 10. The composition ofclaim 1, wherein the elastomer is selected from the group consisting ofhomopolymers of a conjugated diene monomer; and copolymers andterpolymers comprising monomer units selected from conjugated dienemonomers and monomers selected from the group consisting of monovinylaromatic monomers and triene monomers.
 11. The composition of claim 10,wherein the elastomer is selected from the group consisting of isoprene,polystyrene, polybutadiene, butadiene-isoprene copolymer,butadiene-isoprene-styrene terpolymer, isoprene-styrene copolymer,styrene-butadiene copolymer, 1,4-polybutadiene, and vinyl polybutadiene.12. The composition of claim 1, wherein the elastomer contains afunctional group derived from a polymerization terminating agent. 13.The composition of claim 12, wherein the terminating agent has theformula (R₁)_(a) ZX_(b), wherein Z is tin or silicon, R₁ is selectedfrom the group consisting of an alkyl having from about 1 to about 20carbon atoms; a cycloalkyl having from about 3 to about 20 carbon atoms;an aryl having from about 6 to about 20 carbon atoms; and an aralkylhaving from about 7 to about 20 atoms; X is a halogen or an alkoxygroup; “a” is from 0 to 3, and “b” is from 1 to 4, and a+b=4.
 14. Thecomposition of claim 1, wherein the sulfur is selected from the groupconsisting of soluble sulfur, polymeric polysulfide, insoluble polymericsulfur, and mixtures thereof.
 15. The composition of claim 1, whereinthe composition further comprises an additional processing aid selectedfrom the group consisting of esters of fatty acid of hydrogenated C₅ orC₆ sugars, fatty acid esters of non-hydrogenated C₅ or C₆ sugars,polyoxyethylene derivatives of said hydrogenated and non-hydrogenated C₅or C₆ sugars, esters of polyols, and mixtures thereof.
 16. Thecomposition of claim 15, wherein the additional processing aid ispresent in an amount of about 0.1% to about 60% by weight based on theweight of the silica.
 17. The composition of claim 15, wherein theadditional processing aid is fully or partially supported on thereinforcing filler.
 18. The composition of claim 1, wherein thecomposition further comprises an additional filler selected from thegroup consisting of clay, talc, aluminum hydrate, mica, urea and sodiumsulfate.
 19. The composition of claim 18, wherein the additional filleris present in the amount of about 0.5 to about 40 parts by weight perhundred parts of the elastomer.
 20. The composition of claim 18, whereinthe amide compound is supported fully or partially on the additionalfiller.
 21. A process for the preparation of a vulcanizable elastomericcomposition comprising the steps of: a) mixing an elastomer with areinforcing filler comprising silica or a mixture thereof with carbonblack, a processing aid comprising an amide compound having a polar endthat is weakly chemically reactive with the silica and a non-polar endthat is weakly chemically reactive with the elastomer, a cure agent, andan effective amount of sulfur to achieve a satisfactory cure of thecomposition; and b) effecting vulcanization.
 22. The process of claim21, wherein the amide compound is selected from the group consisting ofamide compounds having the formula

wherein R is selected from the group consisting of primary, secondaryand tertiary alkyl groups having 1 to about 30 carbon atoms, alkarylgroups having about 5 to about 30 carbon atoms, and cycloaliphaticgroups having about 5 to about 30 carbon atoms; R′ and R″ are the sameor different from each other and are selected from the group consistingof hydrogen, C₁ to about C₃₀ aliphatic, and about C₅ to about C₃₀cycloaliphatic; R and R′ may be linked together to form a ringstructure; and R′ and R″ may be linked together to form a ringstructure.